Static Compression Device

ABSTRACT

A Static Compression Device (SC device) for active, measurable compression of a fusion graft by the surgeon at the time of surgery is disclosed. The SC device is attachable to adjacent vertebral bodies or other pieces of bone and has a device that applies compressive force to the adjacent vertebral bodies or pieces of bone to assist fusion according to Wolff&#39;s law. The SC device has a locking mechanism that maintains the compression applied at surgery, but prevents further compression (settling) from occurring after surgery. The SC device allows the surgeon the ability to compress a segment, measure the applied compression, and lock the segment in the compressed position. In one embodiment of the invention, the pressure is applied to the SC device through a compression device that applies a desired and measurable amount of force. In this embodiment, the combination of the SC device with a pressure applying and measuring device allows the surgeon more control over the force applied to a cervical, thoracic or lumbar implant than has previously been available. In the preferred embodiment, the SC device compresses two or more adjacent vertebrae across an adjacent bone graft to facilitate fusion of these vertebrae to treat pain produced by pressure from the disks between such vertebrae bulging and resulting in contact with and pressure on the spinal cord and adjacent nerve roots. In other embodiments, the SC device may be used to apply measurable compression across any type of bony interface (e.g. fractures) to facilitate union.

RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 12/522,147,which is a US 371 National Stage Entry of PCT/US07/06830 filed Mar. 20,2007 which claims the benefit of priority from Provisional ApplicationSer. No. 60/788,607 filed Apr. 3, 2006. Each of the aforementionedapplications is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to devices and methods to compress twoor more adjacent S vertebrae across an adjacent bone graft to facilitatefusion of these vertebrae to treat pain produced by pressure from thedisks between such vertebrae bulging and resulting in contact with andpressure on the spinal cord and adjacent nerve roots.

2. Description of Related Art

For nearly half a century, anterior cervical discectomy and fusion hasbeen performed for 0 individuals complaining of intractable upperextremity pain due to cervical disc herniation or bone spurs at singleor multiple levels. This procedure has undergone several significantmodifications since its inception. The introduction of theSmith-Robinson technique of using tricortical iliac crest bone graft,the technique of denuding vertebral endplates of cartilage described byZdeblick et al., and the present use of cervical plates have allrepresented significant technical advances which have increased fusionrates and 5 improved patient outcomes. Currently it is possible toexpect greater than 85% good or excellent outcomes for individuals withappropriate indications who undergo this surgical procedure.

However, several problems remain. Although fusion rates for one levelanterior cervical fusion with autograft (patient's own bone) mayapproach 95%, these rates decrease significantly for each additionallevel incorporated in the fusion. Additionally, using autograft bonetypically involves the use 0 of a second incision, which significantlyincreases patient morbidity. Allograft bone (bone from another human) isa viable option, but has considerably lower fusion rates than autograftand is generally not considered a good choice in multiple level fusionsurgery.

The use of anterior cervical plates has been credited with increasingfusion rates in multiple level fusions. It is thought that the immediatestability provided by the plate provides a more favorable environmentfor fusion to occur. The vast majority of plates on the market providefor static stabilization of the vertebral body-graft construct (nocompression, no dynamization). More recently dynamic plates have beenintroduced. These plates provide for passive dynamic compression of thevertebral body-graft construct. This compression occurs postoperativelywhen the weight of the patient's head loads the construct, allowing forpassive compression of the graft to occur. Wolff's law (The concept thatbone heals best under compression) suggests that the use of dynamiccompression plates should lead to increased fusion rates. However, thishas not been found to be the case. Several studies have indicated thatdynamic compression plates do not lead to higher fusion rates thanstatic plates. In addition, the possibility of uncontrolled settlingover time which may lead to kyphosis (reversal of the normal curvatureof the neck) has caused these plates to fall out of favor with manysurgeons.

Wolff's law is a well-accepted orthopedic principle, championed andreported in the trauma literature by the Swiss AO Foundation, anon-profit surgeon-driven organization dedicated to progress inresearch, development, and education in the field of trauma andcorrective surgery. Several studies have shown that long bones heal bestunder rigid compression. This has lead to the development of specialcompression plates that are currently widely used in surgical techniquesof open reduction and internal fixation of fractures.

It is believed that there is no plate on the market that truly invokesWolff's law in spinal fusion surgery by providing rigid static loadingof the graft-vertebral body construct. Mechanisms for achievingcompression on adjacent vertebrae are known. But, most of these deviceseither utilize compression across individual screws (risking cut out dueto lessened surface area) or attempt to achieve compression prior to theplate being applied (making this a cumbersome technique).

SUMMARY OF THE INVENTION

The Static Compression Device (SC device) of the present inventionallows for active, measurable compression of a fusion graft by thesurgeon at the time of surgery. The SC device is attachable to adjacentvertebral bodies or other pieces of bone and has a device that appliescompressive force to the adjacent vertebral bodies or other pieces ofbone to assist fusion according to Wolff's law. The SC device has alocking mechanism that maintains the compression applied at surgery, butprevents further compression (settling) from occurring after surgery.So, the SC device allows the surgeon the ability to compress a segmentor other adjacent pieces of bone, measure the applied compression, andto lock the segment or pieces of bone in the compressed position. In oneembodiment of the invention, the pressure is applied to the SC devicethrough a compression device that applies a desired and measurableamount of force. In this embodiment, the combination of the SC devicewith a pressure applying and measuring device allows the surgeon morecontrol over the force applied to a cervical, lumbar or thoracic implantor implant applied to other pieces of bone than has previously beenavailable. The SC device of the present invention in one embodimentcompresses two or more adjacent vertebrae across an adjacent bone graftto facilitate fusion of these vertebrae to treat pain produced bypressure from the disks between such vertebrae, adjacent bone spurs orboth bulging and resulting in contact with and pressure on the spinalcord and adjacent nerve roots or any other disorder of the spine. Thevertebrae may be in the cervical, thoracic or lumbar spine. In fact, invarious embodiments, the SC device may be used to apply measurablecompression across any type of bony interface (e.g. fractures) tofacilitate union.

The SC device has four unique characteristics which together provide forstatic compression of the vertebral body-graft interface:

The use of fixed angle screws to secure the SC device to the vertebralbodies;

The use of a compression device to apply and measure the pressureapplied to the vertebral bodies by the SC device;

The technique of using active, static compression to assist the fusionprocess; and

The use of a locking mechanism that maintains compression during thefusion process to facilitate bone growth.

This SC device differs from currently known static plates by providingcontrolled loading (compression) of the graft at the time of surgery.The SC device also differs from currently known dynamic plates in thatthe compression achieved is “static” (rigid) and prevents further“dynamic” settling from occurring after the procedure is completed. Theresulting major advantage of the SC device over previously known Sdevices is that the SC device may significantly increase fusion rates(especially in multiple level cervical fusion) and maintain the anatomyof the cervical spine (preventing excessive compression leading tokyphosis). In fact, it is believed that using the SC device to providestatic loading at each level in multiple level fusions may allow the useof allograft bone to approach fusion rates now only attainable by usingautograft techniques. 0 The invention will be described hereafter indetail with particular reference to the drawings.

Throughout this description, like elements, in whatever embodimentdescribed, refer to common elements wherever referred to and referencedby the same reference number. The characteristics, attributes,functions, interrelations ascribed to a particular element in onelocation apply to that element when referred to by the same referencenumber in another location unless specifically stated otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of one embodiment of the static compressiondevice of the present invention.

FIG. 2 is a top view of the static compression device of FIG. 1.

FIG. 3 is a bottom view of the static compression device of FIG. 1.

FIG. 4 is a side view of the static compression device of FIG. 1.

FIG. 5 is a bottom end view of the static compression device of FIG. 1.

FIG. 6 is a perspective view of the male plate of the static compressiondevice of FIG. 1.

FIG. 7 is a side view of the male plate of the static compression deviceof FIG. 1.

FIG. 8 is a top view of the male plate of the static compression deviceof FIG. 1.

FIG. 9 is a bottom end view of the male plate of the static compressiondevice of FIG. 1.

FIG. 10 is a perspective view of the female plate of the staticcompression device of FIG. 1.

FIG. 11 is an end view of the female plate of the static compressiondevice of FIG. 1.

FIG. 12 is a bottom view of the female plate of the static compressiondevice of FIG. 1.

FIG. 13 is a perspective view of the interconnecting plate of the staticcompression device of FIG. 1.

FIG. 14 is a top view of the interconnecting plate of the staticcompression device of FIG. 1.

FIG. 15 is a perspective view of the static compression device of FIG. 1in an embodiment without the interconnecting plate.

FIG. 16 is a perspective view of the static compression device of FIG.1S in an unlocked configuration.

FIG. 17 is a perspective view of the static compression device of FIG.15 in a locked configuration.

FIG. 18 is a perspective view of the locking clamp of the staticcompression device of FIGS. 1 and 15.

FIG. 19 is a side view of the locking screw of the static compressiondevice of FIG. 1.

FIG. 20 is a perspective view of one embodiment of the compression toolof the present invention.

FIG. 21 is a perspective view of the embodiment of the compression toolof FIG. 20 from the opposite side of the view of FIG. 20.

FIG. 22 is a perspective view of the preferred embodiment of thecompression tool of the present invention with cannula for receiving ascrewdriver.

FIG. 23 is a close up perspective view of the distal end of thecompression tools of the present invention.

FIG. 24 is a perspective view of another embodiment of the compressiontool of the present invention.

FIG. 25 is a side view of the embodiment of the compression tool of FIG.24.

FIG. 26 is an exploded perspective view of the turnbuckle of theembodiment of the compression tool of FIG. 24.

FIG. 27 is an exploded perspective view of the compression tool of FIG.24.

FIG. 28 is a perspective view of an embodiment of the static compressiondevice of the present invention.

FIG. 29 is a perspective view of the static compression device of FIG.28 without the locking screw in place.

FIG. 30 is a side view of the locking screw of the static compressiondevice of FIG. 28.

FIG. 31 is a cross-sectional perspective view of the static compressiondevice of FIG. 28 without the locking screw in place.

FIG. 32 is a perspective view of the static compression device of FIG.28 without an alternate embodiment of the locking screw in place.

FIG. 33 is a perspective view of an alternate embodiment of the staticcompression device.

FIG. 34 is an end view of the female plate of the static compressiondevice of FIG. 33 with the locking screw and cam in place.

FIG. 35 is a perspective view of the locking screw and cam of the staticcompression device of FIG. 33.

FIG. 36 is a perspective view of one embodiment of the staticcompression device of the present invention.

FIG. 37 is a top view of the static compression device of FIG. 36.

FIG. 38 is a bottom view of the static compression device of FIG. 36.

FIG. 39 is a side view of the static compression device of FIG. 36.

FIG. 40 is a bottom end view of the static compression device of FIG.36.

FIG. 41 is a top end view of the static compression device of FIG. 36.

FIG. 42 is a perspective view of the male plate of the staticcompression device of FIG. 36.

FIG. 43 is a side view of the male plate of the static compressiondevice of FIG. 36.

FIG. 44 is a bottom view of the male plate of the static compressiondevice of FIG. 36.

FIG. 45 is a perspective view of the female plate of the staticcompression device of FIG. 36.

FIG. 46 is an end view of the female plate of the static compressiondevice of FIG. 36.

FIG. 47 is a bottom view of the female plate of the static compressiondevice of FIG. 36.

FIG. 48 is a perspective view of the male plate and female plate of thestatic compression device of FIG. 36 in an interconnected relationship.

FIG. 49 is a perspective view of the male plate and female plate of thestatic compression device 0 of FIG. 36 in an interconnected relationshipand with the locking plate in place.

FIG. 50 is a perspective view of the male plate and female plate of thestatic compression device of FIG. 36 in an interconnected relationshipand with the locking plate and locking screw in place.

FIG. 51 is a top view of the static compression device of FIG. 36 withthe male plate interconnected to the female plate and with the lockingplate in place and in the uncompressed position.

FIG. 52 is a top view of the static compression device of FIG. 36 withthe male plate interconnected to the female plate and with the lockingplate in place and in the compressed position.

FIG. 53 is a bottom view of the locking plate of the static compressiondevice of FIG. 36.

FIG. 54 is a side view of the locking screw of the static compressiondevice of FIG. 36.

FIG. 55 is a perspective view of an alternate embodiment of the staticcompression device.

FIG. 56 is a perspective view of the static compression device of FIG.55 with the guide plate shown in phantom.

FIG. 57 is a perspective view of a series of trial spacers andcorresponding handle of one aspect of the present invention.

FIG. 58 is a perspective view of an embodiment of the static compressiondevice designed to be 5 used in the thoracic or lumbar region of thespine.

FIG. 59 is a perspective view of an embodiment of the static compressiondevice designed to be used to treat fractures.

DETAILED DESCRIPTION OF THE INVENTION

The SC device 10 in a preferred embodiment shown in FIGS. 1-14 and 18has five main parts, a male plate 12, a female plate 14, aninterconnecting plate 15, a locking clamp 16 and a locking screw 18that, in combination with standard cancellous bone screws (not shown)fix the SC device 10 to the patient's vertebrae. The SC device 10 has atop side 20, a bottom side 22 and opposed medial sides 24.

The male plate 12 has a male main body 26 and a central protrusion 28extending away from the male main body 26. The central protrusion 28 hasa top surface 30, a longitudinal axis 32, a bottom surface 33 andparallel sides 36. Central protrusion 28 also has a threaded whole 35 inthe top surface 30.

The male plate 12 also has a pair of side protrusions 29 extending awayfrom the male main body 26 on opposite sides of the central protrusion28. Each of the side protrusions 29 has an inner surface 37 and an outersurface 39. The inner surfaces 37 are directed toward the centralprotrusion 28 and are preferably curved in a concave fashion to matewith the outer surfaces 63 of the left guide 58 and right guide 60 ofthe interconnecting plate 15 or the female plate 14 as will be describedhereafter.

The male main body 26 is relatively flat with a top side 34 and a bottomside 36 and, in a preferred embodiment, has two screw receiving holes38. The screw receiving holes 38 each have a bowl-shaped basin 40 on thetop side 34 to receive the heads of the screws 43 and a through whole 42through which the main body of the screws 43 pass to come into contactwith the vertebral body. The throughholes 42 are configured in a mannerthat allows the cancellous bone screws 43 to be rigidly fixed to theplate once inserted in bone. The method of fixing the screws 43 to theplate may utilize any number of mechanisms well understood in the artthat allow the screws 43 and the male plate 12 to maintain a rigidrelationship once the screws 43 are inserted in bone.

The bottom side 36 of the male plate 12, female plate 14 andinterconnecting plate 15 is preferable roughened, thereby allowing thebottom side 22 of the SC device 10 to “grip” the vertebral body when thebottom side 22 of the SC device 10 is brought into contact with andsecured to the vertebral body by the interaction of the screws 43 andthe body of the SC device 10 as described herein.

As mentioned, the male plate 12 has a central protrusion 28 with a topsurface 30 and a longitudinal axis 32. Central protrusion 28 isdimensioned to mate with and secure the male plate 12 with theinterconnecting plate 15 or the female plate 14 as will be described indetail hereafter. Where the interconnecting plate 15 is used, thecombined length of the central protrusion 28 on the male plate 12 andthe central protrusion 28′ on the interconnecting plate 15 will beslightly longer than the distance the SC device 10 in intended toprovide compression over.

Central protrusion 28 has a boss 44 extending entirely through itapproximately parallel to the top surface 30 that is designed to matewith a relief cut 62 in the interconnecting plate 15/female plate 14.

The interconnecting plate 15 combines the features of the male plate 12and the female plate 14 on its opposite ends. As a result, on one end ofinterconnecting plate there is a central protrusion 28′ essentially asdescribed in connection with the central protrusion 28 of male plate 12.On the opposite end of interconnection plate 15, there is a protrusionreceiving channel 56 essentially as described hereafter in connectionwith the protrusion receiving channel 56 of female plate 14. Inaddition, interconnecting plate 15 has at least a pair of screwreceiving holes 38 essentially as described in connection with the screwreceiving holes 38 of the male plate 12.

The purpose of the interconnecting plate 15 is to allow the SC device 10to be secured to three or more adjacent vertebrae and allow the SCdevice 10 to apply compression across these vertebrae to facilitatehealing as described herein. As a result, a single interconnecting plate15 may be placed between the male plate 12 and the female plate 14 andattached to the vertebra between the vertebrae that the male and femalesplates 12, 14 are attached to. Alternately, several interconnectingplates 15 can be connected end to end (i.e., the protrusion receivingchannel 56 of one interconnecting plate 15 receives the centralprotrusion 28′ of an adjacent interconnecting plate 15 and the processcontinues until all the interconnecting plates 15 are joined together)to form an interconnecting span with a male plate 12 and a female plate14 attached to the ultimate ends of this chain of interconnecting plates15. In this embodiment of the invention, each of the interconnectingplates 15 would have screw receiving holes 38 allowing eachinterconnecting plate 15 to be attached to a single vertebra by bonescrews 43. In a variant of this embodiment, a single interconnectingplate 15 could have several sets of screw receiving holes 38 so thatthis single interconnecting plate 15 could be attached to severaladjacent vertebrae or could span a previously fused segment.

The female plate 14 has a female main body 52 with a bottom side 54 anda protrusion receiving channel 56. Protrusion receiving channel 56 isformed between a left guide 58 and a right guide 60 that extend awayfrom the female main body 52. Left guide 58 and right guide 60 each havean inner surface 61, an outer surface 63, a bottom surface 65 and a topsurface 67. Left guide 58 and right guide 60 are basically rectangularin cross-section with inner surfaces 61 being preferably essentiallyplanar and with outer surfaces 63 being essentially outwardly curvedwith a series of ridges 71 extending outwardly. On the bottom surface 65of the left and right guides 58, 60 facing the protrusion receivingchannel 56, there is a relief cut 62 machined to accept the boss 44 onthe central protrusion 28′ of the interconnecting plate 15 or the maleplate 14.

Protrusion receiving channel 56 is dimensioned to snugly receive thecentral protrusion 28′ with the locking clamp 16 in place on the centralprotrusion 28′ as will be described hereafter so that the centralprotrusion 28′ is “captured” and held in the protrusion receivingchannel 56 by physical contact between the outer surface of the lockingclamp 16 and the inner surfaces of the left guide 58 and right guide 60as well as by the interaction between the central protrusion 28′ and theboss 44 on the inferior aspect of the central protrusion 28′ and reliefcut 62.

The outer surfaces 63 of the left and right guides 58, 60 contact theinner surfaces 37 of the side protrusions 29 under the influence of thelocking clamp 16, as will be described hereafter, to securely locate thefemale plate 14 with respect to the interconnecting plate 15 and theinterconnecting plate 15 with the male plate 12.

The female plate 14, also in a preferred embodiment, has two screwreceiving holes 82. These screw receiving holes 82 receive standardcancellous bone screws 43 that are threaded into the bone of thevertebrae. In similar fashion to screw receiving holes 38, the screwreceiving holes 82 also have a bowl-shaped basin 84 on the upper surface78 to receive the heads of the bone screws 43 and a throughole 86through which the main body of the bone screws 43 pass to come intocontact with the vertebral body. The throughholes 86 are configured in amanner that allows the cancellous bone screws 43 to be rigidly fixed tothe plate once inserted in bone by the interaction of the screws 43 withthe basins 84. The method of fixing the screws 43 to the female plate 14may utilize any number of mechanisms well understood in the art thatallow the screws 43 and the female plate 14 to maintain a rigidrelationship once the screws 43 are inserted in bone.

The SC device 10 has a locking mechanism 88. Locking mechanism 88converts “active” compression applied by the surgeon using thecompression device 90 described below interacting with the SC device 10at the time of surgery to “static” compression after surgery. Thelocking mechanism 88 also provides rigid fixation to the SC device 10 tooptimize bone healing and preventing further settling from occurring.

The locking mechanism 88 in one embodiment includes locking clamp 16 andlocking screw 18. The locking clamp 16 has a top surface 92 with a hole93 extending through it, a bottom surface 94, parallel sides 96, alongitudinal axis 97 and an inner channel 99 between the parallel sides96 and below the top surface 92. The inner width of the inner channel 99of the locking clamp 16 (i.e., the inside distance between the parallelsides 96) is such that the locking clamp 16 will fit snugly over thecentral protrusion 28. The width of the locking clamp 16 (i.e., thedistance between the parallel sides 96) is such that the locking clamp16 will fit snugly between the left and right guides 58, 60 in theprotrusion receiving channel 56.

A single large locking screw 18, dimensioned to rotate freely within thehole 93 of the locking clamp 16, activates the locking mechanism 88. Inthe embodiment of the invention shown in FIGS. 1-19, the locking screw18 has a head 106, a body 108 and a distal end 110 opposite the head106. The head 106 has a larger cross-sectional diameter than thethreaded body 108. The body 108 is threaded at least on the distal end110 to correspond to the threads of the threaded hole 35 in theprotrusion 28.

The parallel sides 96 of locking clamp 16 preferably have a series ofridges 46 and valleys 48, preferably placed substantially perpendicularto the longitudinal axis 97 and tapered from top to bottom, to locateand affix the locking clamp 16 to the inner surfaces of the left guide58 and right guide 60 of the interconnecting plate 15 and female plate14. Through this configuration, the ridges 46 and valleys 48 on thesides 96 of the locking clamp 16 preferably contact and engage with theinner surfaces of left and right guides 58, 60 in frictional ormechanical contact to precisely locate and affix the locking clamp 16within the protrusion receiving channel 56. Because the series of ridges46 and 48 are tapered, as the series of ridges 46, 48 are moved intocontact with and engage the inner surfaces of left and right guides 58,60, this engagement adds compressive force to the adjacent vertebralbodies through the SC device 10. The locking clamp 16 is preferably madeof a material that is harder than the material of the interconnectingplate 15 or the female plate 14.

The present invention also includes a compression device 90 (FIGS.20-23) that allows the surgeon to provide active, controlled compressionbetween the two sliding components of the SC device 10 (male plate 12and female plate 14) at the time of surgery. This compression device 90allows the surgeon to accurately measure the force applied across thegraft by the SC device 10 and allows the surgeon to stop compressingwhen a predetermined amount of force has been obtained. Since both themale plate 12 and the female plate 14 are each connected to adjacentvertebral bodies by two fixed angle bone screws 43, this provides foreven, surgeon-controlled compression across the interbody graft.

The compression device 90 has two arms 114, 116 that each have a handle118, 120 at one end and a foot 122, 124, located at a distal end 126,128, respectively. The arms 114, 116 are connected via a pivot 130 thatconnects the respective arms 114, 116 and allows them to move inscissors-like movement with respect to each other. By connecting thearms 114, 116 through a pivot 130, a surgeon squeezing the handles 118,120 moves the distal ends 126, 128 together. By connecting these distalends 126, 128 to the SC device 10, a surgeon squeezing the handles 118,120 together is able to apply compression to the SC device 10 and thusto adjacent vertebral bodies through the interaction of the feet 122,124 and the male plate 12 and female plate 14 as will be explainedhereafter.

Each foot 122, 124 of the compression device 90 engages the male plate12 or female plate 14 (or interconnecting plate 15), respectively, toapply pressure to move the male plate 12 and female plate 14 toward eachother as the physician squeezes the handles 118, 120 together. In theembodiment of compression device 90 and SC device 10 shown in FIG. 23,the distal ends 126, 128 of feet 122, 124, respectively, are shaped withpins 132 that protrude from the distal ends 126, 128.

In the embodiment shown in FIGS. 21-23, pins 132 protrude from adaptorplates 134 having throughholes 136. Adaptor plates 134 are secured tothe distal ends 126, 128 of feet 122, 124, respectively by screws 138that pass through throughholes 136. The distal ends 126, 128 of feet122, 124, respectively each have a threaded secure hole 140 thatreceives a screw 138. In this way, adaptor plates 134 are secured to thedistal ends 126, 128 of feet 122, 124, respectively. The adaptor plates134 may be removed and replaced with hooks protruding from the distalends 126, 128 of feet 122, 124, respectively, that each engage a slot onthe outermost aspects of the male and female plates 12, 14 placed orformed in the top side 34 of the male plate 12 and the top surface 78 ofthe female plate 14. This enables the ends of compression device 90 tobe modular (i.e., replaceable so that the appropriate end for a desiredapplication can be placed on the compression device 90) with respect tousing different techniques to achieve compression.

The male plate 12 and female plate 14 each have a notch 142, 144,respectively, located on opposite ends of the SC device 10 and shaped toreceive the pins 132 in a snug, conforming fashion so that compressionapplied to the feet 122, 124 by squeezing the handles 118, 120 togetheris transferred from the distal ends 126, 128 to the male plate 12 andfemale plate 14, respectively, through the interaction of the pins 132with the notches 142, 144.

In an alternate embodiment of the invention, the distal ends 126, 128 offeet 122, 124, respectively, again engage the male plate 12 and thefemale plate 14, respectively, through pins 132. However, in thisembodiment, the notches 142, 144 are located in the outer edge of thetop surfaces 26 and upper surface 78 of the male plate 12 and femaleplate 14, respectively, sized and shaped to receive the pins 132 in asnug fashion so that compression applied to the feet 122, 124 bysqueezing the handles 118, 120 together is transferred from the pins 132to the male plate 12 and female plate 14, respectively, through thenotches 142, 144.

The compression device 90 also preferably has a gauge 146 that allowsthe physician to measure the compression force being applied to the SCdevice 10, and thus to the vertebral bodies, by the squeezing togetherof the handles 118, 120. The gauge 146, by quantifying the deflectionthe handles 118, 120 when they are squeezed together, gives an accuratemeasurement of force applied across the SC device 10. In the embodimentof the compression device 90 shown in FIG. 20, gauge 146 includes an arm148 attached to pivot 130 and located between handles 118, 120. The arm148 preferably has a circular, oval, square or rectangular cross-sectionand a horizontal and a vertical component 149, 151, respectively. Theaim 148 has indicia ISO located on at least a portion of the horizontalcomponent 149.

The gauge 146 has an indicator 152 that is an annular spacer locatedalong the horizontal component 149 of arm 148. The indicator 152 has acentral opening 154 sized to be approximately the same size and shape asthe cross-sectional size and shape of the horizontal component 149 ofarm 148 so that indicator 152 is attached to the horizontal component149 by sliding the horizontal component 149 through the first centralopening 154. A frictional fit between the first central opening 154 andthe horizontal component 149 holds the indicator 152 in position on thehorizontal component 149.

As mentioned above, when the handles 118, 120 are squeezed together, theresulting amount of deflection of the handles 118, 120 is directlyrelated to the force applied by the physician as he or she squeezes thehandles 118, 120 together. Because the vertical component 151 of the arm148 is rigidly attached to the pivot 130, as the handles 118, 120 movetogether as a result of being squeezed, the horizontal component of thearm 148 and its associate indicator 152 does not move. As a result, thehandle 120 will be deflected along the horizontal component 149 of thearm 148 and along the indicia 150 located on the horizontal component149. By observing the location of the handle 120 with respect to theindicia 150 on the horizontal component 149, the amount of force appliedto handles 118, 120 and, therefore to the distal ends 126, 128 of feet122, 124, is indicated. When the distal ends 126, 128 are placed infunctional contact with the notches 142, 144 of the male plate 12 andfemale plate 14, the gauge 146 indirectly measures the compression beingapplied to the graft, and allows the surgeon to stop compressing once apredetermined force has been achieved.

By placing the indicator 152 at a desired location on the horizontalcomponent 149 of arm 148, the physician can squeeze the handles 118, 120together until the handle 120 moves into contact with the indicator 152.At this point, the physician knows that the desired amount offered hasbeen applied to the compression device 90 and thereby to the device 10to the graft

In another embodiment of the compression device 90 shown in FIG. 22,gauge 146 again includes an arm 148. But, in this embodiment, the arm148 is connected to a rigid arm 156 located on the outside of handle118. Rigid arm 156 is attached to handle 118 near the pivot 130. Arm 148extends from the rigid arm 156 in the direction that handle 118 moveswhen it is squeezed together with handle 120 and may extend through aslot in handle 118 or may be formed around handle 118 so that arm 148extends toward handle 120. In this embodiment as well, indicator 152 islocated between handles 118, 120.

As mentioned above, when the handles 118, 120 are squeezed together, theresulting amount of deflection of the handles 118, 120 is directlyrelated to the force applied by the physician as he or she squeezes thehandles 118, 120 together. Because the arm 148 is rigidly attached tothe rigid arm 156, as the handle 118, 120 move together as a result ofbeing squeezed, the arm 148 and its associate indicator 152 does notmove. As a result, the handle 118 will be deflected along arm 148 andalong the indicia 150 located on arm 148. By observing the location ofthe handle 118 with respect to the indicia 150 on arm 148, the amount offorce applied to handles 118, 120 and, therefore to the distal ends 126,128 of feet 122, 124, is indicated. When the distal ends 126, 128 areplaced in functional contact with the notches 142, 144 of the male plate12 and female plate 14, the gauge 146 indirectly measures thecompression being applied to the graft, and allows the surgeon to stopcompressing once a predetermined force has been achieved. Again, byobserving the location of the handle 118 versus the indictor, thesurgeon will know that the desired amount of force has been applied tothe compression device 90 and thereby to the SC device 10 to the graft.

An alternative embodiment of the compression device 90 is referred to asthe static compensating compressor 590 and shown in FIGS. 24-27. Thestatic compensating compressor 590 utilizes a force indicator 592 and amethod to measure static compressive forces applied by the patient's ownanatomy to allow the surgeon to factor the patient's own staticcompressive forces out to ensure the correct value of the absolutecompression applied through the SC device 10 to the vertebral bodies.The static compensating compressor 590 includes a turnbuckle 594 thatuses a threaded nut 596, threaded inserts 598, along with a series ofcompression springs 600 and guide rods 602, collectively known as thedistraction mechanism 604, to allow the surgeon to apply a measurabledistraction force (a force in the opposite direction to the compressiveforce) to unload the vertebral segment. By unload, we mean to takecompression pressure, usually applied by the patient's own muscles andligaments, off the vertebral segments. Once compression pressure on thevertebral segment has been unloaded from the vertebral segment, a nullpoint (i.e., a point where there is no compression or distraction forceon the vertebral bodies) is established and therapeutically usefulcompression can be applied to the vertebral segment at a known rate.

The force indicator 592 has a central processing unit (CPU) 606 and adisplay 608 to determine and indicate the amount of force applied ineither compression or distraction to the SC device 10 and a zeroingfunction that allows the surgeon to compensate for static anatomicalcompression. The force indicator 592 also includes a strain gauge 610.The force indicator 592 is a simple electronic device that measures theresistance across the strain gauge 610 that is secured to one of thearms 114, 116 of the compressor 90 and then uses the CPU 606 todetermine, by formula or through a lookup table, and indicate the amountof force applied by the compressor 90 and then indicate this amount offorce on the display 608. The CPU 606 may be an application specificintegrated circuit (ASIC), a digitally based central processing unit ordiscrete components.

The display 608 is preferably attached to one of the handles 118, 120 ofthe arms 114, 116 and the CPU 606 and the display 608 are preferablycombined into a single unit However, either or both the CPU 606 and thedisplay 608 may be located remotely from the static compensatingcompressor 590 and the CPU 606 and the display 608 may be locatedseparately from each other.

The strain gauge 610 is preferably located on a distal end 126, 128 of arespective arm 114, 116 of the compression device 90 although the straingauge may be located anywhere on an arm 114, 116 or on the pivot 130. Asthe physician applies compression through the compression device 90 tothe SC device 10 and thus to the vertebral bodies by squeezing thehandles 118, 120 of the compression device 90 together, the distal ends126, 128 will flex or bend slightly. The strain gauge 610 measures thisflexing or bending of the distal ends 126, 128 and communicates thevalue to the CPU 606 where the force value, once determined, indicatesthe amount of force applied to the SC device 10, and thus to thevertebral bodies, as is well understood in the art.

As mentioned above, the static compensating compressor 590 is able toapply distraction pressure to the vertebral bodies through the use of aturnbuckle 594 (FIG. 26). The threaded nut 596 has a pair of threadedholes 612. The threaded holes 612 are threaded in opposite directions(i.e., with right and left handed threads) as is well understood inturnbuckles. The threaded inserts 598 each have a threaded end 614 and anon-threaded end 616 to which a guide rod 602 is attached. The guiderods 602 are preferably attached to the non-threaded ends 616 throughsprings 600 that have a low spring force. Springs 600, when used, applya low biasing force to the turnbuckle 594 to remove looseness in theconnection between the turnbuckle 594 and the arms 114, 116. In anotherembodiment, the guide rods 602 may be attached directly to thenon-threaded ends 616. The threaded inserts 598 are also each threadedon their threaded ends 614 in opposite directions (i.e., with right andleft handed threads) and are mated with the threaded holes 612 of thethreaded nut 596 so that as the threaded nut 596 is rotated in a firstdirection, the threaded inserts 598 are drawn into the threaded holes612 and as the threaded nut 596 is rotated in a second direction, thethreaded inserts 598 are moved out of the threaded holes 612. As aresult, as the threaded nut 596 is rotated in a first direction, theturnbuckle 594 expands in length and as the turnbuckle 594 is rotated ina second direction opposite the first direction, the turnbucklecontracts in length.

The turnbuckle 594 is preferably attached between and applies a preloadto the handles 118, 120 of the arms 114, 166 of the compressor 90.However, the turnbuckle 594 may also be attached between and apply apreload to the distal ends 126, 128 of the arms 114, 166 of thecompressor 90. In either embodiment, the turnbuckle 594 is fittedbetween the arms 114, 116, either between the handles 118, 120 or distalends 126, 128 preferably in slots 618, secured with pins 620 or othersuitable retaining devices well understood in the art In a variant ofthis embodiment, the pins 620 could be quick release pins, allowing theturnbuckle 594 to be quickly removed once the null point is found, asexplained below, so that the compressor 90 would be used thereafterwithout the turnbuckle 594.

Once the turnbuckle 594 is attached to the arms 114, 116, by turning thethreaded nut 596, the turnbuckle 594 expands or contracts (depending onthe direction the threaded nut 596 is rotated) thereby applying apreload in either a compression or distraction direction to the arms114, 166 of the compressor 90 and thus to the SC device 10 andultimately to the vertebral bodies. This preload allows the vertebralsegment that the SC device 10 is spanning to become unloaded or lifted.By “lifted” or “lift-off” we mean that a distraction force has beenapplied to the vertebral segment by the compressor 90 and SC device 10to the point where the distraction force is equal to the anatomicalcompression force applied to the vertebral segment by the patient's ownmuscles and ligaments. At this point, called the null point, there is anet zero force applied to the affected vertebral segment so that theaffected vertebral bodies separate or “lift-off” of each other slightlywhich separation is visually ascertained by the physician.

Once lift-off has been determined, and consequently, the null pointestablished, a button is pushed on the display 608, on the CPU 606itself or otherwise, including remotely, to alert the CPU 606 thatstrain measured by the strain gauge 610 at that point is the null point.As a result, the CPU 606 directs the display 608 to indicate a zeroreading at that point.

At this point, the turnbuckle 594 is preferably removed from thecompressor 90. As the turnbuckle 594 is removed, the patient'sanatomical compression force will be applied to the affected vertebralsegment. This compression force will be transferred through the SCdevice 10 to the compressor 90 where the strain gauge 610 will measurethe anatomically applied compression force and the CPU 606 will directthe display 608 to indicate the anatomically applied compression force.Thereafter, the surgeon applies an additional compressive force to theSC device 10 which additional compressive force will be sensed by thestrain gauge 610 combined with the compressive force applied by thepatient's own anatomy. As a result, the CPU 606 will determine the totalcompressive force applied to the vertebral segment (i.e., the summationof the patient's own anatomical compressive force and the compressiveforce being applied by the physician by the compressor 90) which totalcompressive force is displayed on the display 608. The physician thenapplies the additional compressive force to the vertebral segment untila desired total compressive force for maximum therapeutic value isobtained.

If the force indicator 592 is set to a null point before distractionpressure is applied to the vertebral segment by the turnbuckle 594, theforce indicator 592 will also indicate the distraction pressure appliedto the vertebral segment by the turnbuckle 594. At the point wherelift-off occurs, the display 608 will indicate the amount of distractionpressure being applied by the turnbuckle 594 which equals the amount ofcompression force that is applied by the patient's own anatomy. Thisamount of compression force is also potentially valuable information inthat the amount of compression force anatomically applied by the patientmay be used by the physician to determine the overall health andstrength of the patient's inherent anatomical compression mechanism.Thereafter, the physician may set the force indicator 592 to zero asdescribed above to indicate the null point for the application ofcompression force also as described above.

In a variant to the embodiments of the compression device 90 describedabove, a small cannula 158 is attached to the compression device 90 atthe pivot 130. The cannula 158 is directed downward toward the SC device10. This cannula 158 is intended to receive a special screwdriver 160that activates the locking mechanism 88 of the SC device 10 when thedesired compression is achieved. The screwdriver 160 is inserted throughthe cannula 158 into the loosened locking mechanism 88 as thecompression device 90 engages the male plate 12 and female plate 14.Thus, it is possible for the surgeon to maintain compression across thegraft with one hand on the compression device 90, to determine thedegree of compression achieved on the SG device 10 by visualizing thecompression gauge 146, and to activate the locking mechanism 88 of theSC device 10 with the other hand, causing the SC device 10 to become arigid construct and preventing further movement of the vertebral bodiesfrom occurring.

Alternately, the physician may use the screwdriver 160 without insertingit through the cannula 158 or may use the screwdriver 160 in anembodiment of the compression device 90 that does not include a cannula158. Further, in any of the embodiments of the compressor 90, thecompressor 90 may be disposable or reusable.

One mechanism of fixing the bone screws 43 to the male plate 12 at arigid predetermined angle is described as follows. As mentioned above,bone screws 43 fix the male plate 12, the female plate 14 and theinterconnecting plate, 15, if present, to the vertebral bodies. The bonescrews 43 may be machined, as is common for such screws, with twoseparate sets of threads, one on the shaft of the screw 43, the secondset on the head of the screw 43. These threads are distinct from eachother in that they have different pitches and distinct outer diameters.The pitch and outer diameter of the threads on the shaft of the screw 43are that of a standard cancellous bone screw. In order to engage themain male plate 12, the diameter of the head 45 of the bone screw 43head is significantly larger than the diameter of the threads on theshaft of the bone screw 43. However, the threads on the bone screw 43are smaller in outer diameter and tighter in pitch than the bore of thescrew receiving holes 38. These threads are machined to engage threadsof similar pitch and diameter in the screw receiving holes 38 of themale plate 12.

The screw receiving holes 38 are machined to project the screw 43 intothe vertebral body at a predetermined angle determined to be mostadvantageous for fixing the device 10 to the vertebral bodies. Thus, byengaging the threads on the head 45 of the screw 43 with those in thescrew receiving hole 38, the screw 43 projects into the vertebral bodyat the predetermined angle and maintains a rigid fixed relationship withthe male plate 12.

The interaction between the bone screws 43 and the SC device 10described above is one of the many ways that bone screws 43 can beconnected to the SC device 10. However, it is well understood in the artthat there are other commercially available ways to connect devices likethe SC device 10 to vertebrae that could also be used. As a result, itis intended that any method of connecting the SC device 10 to vertebralbone so that there is a rigid fixed relationship between the SC device10 and the bone may be used with the SC device 10 of the presentinvention.

The mechanism of fixing the screws 43 to the female plate 14 at a rigidpredetermined angle is similar to the mechanism for fixing the screws 43to the male plate 12 at a rigid predetermined angle as described above.Again, the bone screws 43 are machined, as is common for such screws,with two separate sets of threads, one on the shaft of the screw 43, thesecond set on the head of the screw 43. These threads are distinct fromeach other in that they have different pitches and distinct outerdiameters. The pitch and outer diameter of the threads on the shaft ofthe screw 43 are that of a standard cancellous bone screw. In order toengage the female plate 14, the inner diameter of the screw head 45 issignificantly larger than the inner diameter of the threads on theshaft. However, the threads on the screw head 45 are smaller in outerdiameter and tighter in pitch than the bore of the screw receiving holes82. These threads are machined to engage threads of similar pitch anddiameter in the screw receiving holes 82 of the female plate 14. Thescrew receiving holes 82 are machined to project the screw 43 into thevertebral body at a predetermined angle. Thus, by engaging the threadson the head 45 of the screw 43 with those in the screw receiving holes82, the screw 43 projects into the vertebral body at the predeterminedangle and maintains a rigid fixed relationship with the female plate 14.

The SC device 10 as described in the embodiment above has the option ofusing fixed angle screws. However, variable angle screws 43 may be usedwith the SCD device 10 as long as when these screws 43 are placedthrough the male plate 12, female plate 14 or interconnecting plate 1 Sinto bone, their relationship with the respective plate 12, 14 or 15becomes rigid. There are numerous methods of attaching bone screws toplates well understood in the art, all of which may be used with thisdevice. It is important that the relationship between the screws and theplates 12, 14, 15 becomes rigid once the screws are placed in order toavoid “toggle” of the screws during the compression maneuver. “Toggle”must be avoided, because if it occurs, actual compression may besignificantly less than measured.

Most currently available non-adjustable plates have the option to placescrews into the bone at a variety of different angles to obtain optimumpurchase. While this is necessary to position static plates, it is notnecessary in the SC device 10. In fact the sliding capability that theSC device 10 has in the unlocked arrangement renders the common use ofvariable screws superfluous. Nevertheless, any type of screw may be usedwith the SC device 10 as long as a mechanism exists for rigidly fixingthe screw to the plate.

The importance of having screws 43 that are rigidly fixed to the maleplate 12 and female plate 14 at a predetermined angle is thatcompression occurs through the entire SC device 10 (the slidingcomponents of the SC device 10 (male plate 12 and female plate 14 andthe two rigidly attached screws), rather than through the screwsindividually. Also, as mentioned, the bottom side 36 of the male plate12 and the bottom side 54 of the female plate 14, and of theinterconnecting plate 15 if present, are roughened, allowing the SCdevice 10 to “grip” the vertebral body. These characteristics incombination provide for a much larger surface area to compress against(the contact of the bottom side 36 and bottom side 54 on the anteriorsurface of the vertebrae as well as the two rigidly fixed bone screws inthe male plate 12 and female plate 14, respectively). This results in amuch more even compression against the entirety of the interbody graftand minimizes the potential for screw cutout or bony failure.

For purposes of illustrating the operation of locking mechanism 88 ofthe invention in the embodiment shown in FIGS. 1-14, a variant of theembodiment described above will be used. In this variant, shown in FIGS.15-17, there is no interconnecting plate 15. Instead, the male plate 12and female plate 14 intermesh directly through the interaction of thecentral protrusion 28 and side protrusions 29 of the male plate 12 andthe left and right guides 58, 60 of the female plate 14. In describingthe operation of the SC device 10, it is to be understood that theconcepts described apply as well to the interaction between the maleplate 12 and one end of the interconnecting plate 15 and the interactionbetween the opposite end of the interconnecting plate 15 and the femaleplate 14.

In use, the central protrusion 28 is inserted into the protrusionreceiving channel 56 (FIG. 15). Because protrusion receiving channel 56is dimensioned to receive central protrusion 28 with the locking clamp16 in place, central protrusion 28 is precisely located and retainedwithin the protrusion receiving channel 56. In this position with thelocking clamp 16 in place on the top surface 30 of central protrusion28, the ridges 46 and valleys 48 on the parallel sides 96 of lockingclamp 16 come into loose contact with the inner surface 61 of left guide58 and right guide 60 of the female plate 14. (FIG. 15) The lockingscrew 18 is passed through the screw hole 93 so that its distal end 110comes into contact with and is threaded into the threaded hole 35 asufficient amount to locate the distal end 110 of the locking screw 18in the threaded hole 35 but not a sufficient amount to deform thelocking clamp 16.

Bone screws are passed through the screw receiving holes 38 and 82 andinto the vertebral bone. These bone screws are screwed into thevertebral bone until the heads of the bone screws seat into the basins40, 84 of the male plate 12 and female plate 14, respectively.

The compression device 90 is then used to apply the desired compressionto the SC device 10. The pins 132 are placed in the notches 142, 144 andthe handles 118, 120 are squeezed together. As a result, compressionpressure is applied to the male plate 12, female plate 14 andinterconnecting plate 15 if present, and thereby to the vertebral bonethrough the bone screws.

As mentioned above, where a gauge 146 is present, the amount ofcompressive force applied to the SC device 10 can be ascertained.

As shown in FIGS. 16 and 17, when the male plate 12 is moved into anintermeshing position with the female plate 14 and the appropriateamount of compression is applied to the SC device 10 through thecompression device 90, the screwdriver 160 is coupled to the head 106 ofthe locking screw 18. The screwdriver 160 is rotated so that thethreaded body 108 of locking screw 18 is threaded into the threaded hole35. The locking screw 18 is then screwed further onto the centralprotrusion 28 on the male plate 12 so that the head 106 contacts the topsurface 92 of the locking clamp 16.

Once the head 106 has contacted the top surface 92, further rotation ofthe locking screw 18 will cause the head to be forced into the materialof the top surface 92 of the locking clamp 16. This will cause thelocking clamp 16 to interfere so that the parallel sides 96 will beforced into engaging and locking contact with the inner surfaces 61 ofthe left and right guides 58, 60 on the female plate 14 or theinterconnecting plate 15. This outward compression from the interferencefit is transferred through the left and right guides 58, 60 to causeengaging and locking contact between the outer surface 63 of the leftand right guides 58, 60 and the inner surface 37 of the side protrusions29. The interaction between the head 106 and the screw hole 35 locks thelocking clamp 16 against the right and left guides 58, 60. Once maleplate 12 is secured with respect to the female plate 14, the compressiondevice 90 is removed. As a result, the compression applied to the SCdevice 10 through the compression device 90 will be locked to thevertebral bone through the male plate 12 and female plate 14 (andinterconnecting plate 15 if used) because these various components arelocked in a fixed relationship to each other.

An alternate embodiment of the locking mechanism 88 is shown in FIGS.28-32 and is described as follows. In this embodiment there is nolocking clamp 16 and the locking screw 18 (FIG. 30) is large in diameterand is tapered from the head 106 to the distal end 110 so that thediameter of the head 106 is significantly larger than the diameter ofthe distal end 110. In addition, the diameter of head 106 of the lockingscrew 18 is greater than the width of the central protrusion 28.Further, the threaded hole 35 of the central protrusion 28 of the maleplate 12 is fashioned in a threaded tapered fashion so that the lockingscrew 18 fits into the threaded hole 35. In this embodiment the centralprotrusion 28 may include a slot 41 through which the threaded hole 35passes to allow maximal deformation of the central protrusion 28 alongthe length of the central protrusion 28.

Thus, when appropriate compression has been applied to the vertebralbodies by the SC device 10, the locking mechanism 88 is engaged byadvancing the locking screw 18 into the threaded hole 35. Theadvancement of the locking screw 18 into the threaded hole 35 deformsthe outer aspect of the central protrusion 28 which surrounds thethreaded hole 35 thereby causing this portion of the central protrusion28 to expand and interfere with the inner surface 61 of left guide 58and right guide 60 of the female plate 14. The presence of the slot 41helps the deformation of the outer aspects of the central protrusion 28by making it easier for the two sides of the central protrusion 28 tomove away from the threaded hole 35 under the influence of the lockingscrew 18. This outward compression from the interference betweenexpanded central protrusion 28 and left and right guides 58, 60 istransferred through the left and right guides 58, 60 to cause engagingand locking contact between the outer surfaces 63 of the left and rightguides 58, 60 and the inner surface 37 of the side protrusions 29.

It should be noted that the SC device 10 is a modular and expandabledevice. The characteristics of this device allow it to be disassembledin vivo and expanded to immobilize adjacent vertebral segments (or otherbone pieces or segments) by the insertion of one or more interconnectingplates 15 to form an interconnecting span as described above.

Thus, should subsequent surgery be required, as for example, in the caseof adjacent segment disease (the segment adjacent to a fused segmentundergoing accelerated degeneration), it is not necessary to expose theentirety of the SC device 10 and remove it to extend the fusion to theadjacent segment (as is the case with nearly all current plates).Instead, an end portion of the SC device 10 (e.g., either the male plate12 or female plate 14) may be removed (leaving the remainder of the SCdevice 10 intact), the fusion completed and the SC device 10 simplyexpanded to include the newly fused segment by inserting one or moreinterconnecting plate IS, then reapplying the end portion (either themale plate 12 or female plate 14, respectively) of the SC device 10 tothe newly fused vertebrae, applying compression as explained herein andlocking and securing the SC device 10.

An alternate embodiment of the SC device 10 is shown in FIGS. 33-35. Inthis embodiment, the locking screw 18 of the locking mechanism 88 ismodified to include a cam 162 that rotates around the locking screw 18below the head 106 (FIG. 35). Further, the edges of channel 80 form atrack 164 (FIG. 34) dimensioned to receive and constrain the cam 162within the track 164 in a relatively conformal manner. In addition, inthis embodiment of the locking mechanism 88, there is no locking clamp16 and the central protrusion 28 does not have the protrusion ridges 50.

Cam 162 is relatively disk shaped with elongated opposed outer edges166. The outer edges 166 resemble somewhat a “V” with the bottom of theV being farther from the body 108 than the open mouth of the V whichrotates around the body 108 of locking screw 18. The locking screw 18 inthis embodiment rotates freely with respect to cam 162. However, the camportion can be rotated into contact with and engage the track 164 whenrotated 90 degrees about the body 108. When the locking screw 18 is inthe unlocked position, the male plate 12 is inserted into the protrusionreceiving channel 56. With the cam 162 rotated so that the cam 162 doesnot contact the track 164, the cam 162 and the locking screw 18 moveeasily into the channel 80. Then the male plate 12 and the female plate14 are moved to the desired position relative to each other, the cam 162is rotated 90 degrees so that the cam 162 contacts the wall of the track164 where such frictional contact prevents the male plate 12 from movingrelative to the female plate 14. In addition, though both the lockingscrew 18 and the female plate 14, including the track 164 are preferablymade of titanium, the locking screw 18 is of a significantly hardergrade. In this way, as the locking screw 18 is rotated 90 degrees,because the cam 162 is present and has a cam shape, the cam 162 isforced into the track 164, effectively deforming the cam 162 and forminga “cold weld” with the track 164. In this way, a rigid, permanentfixation between the locking screw 18 and the male plate 12 to which itis attached and the female plate 14 through track 164 is achieved andcompression is maintained. The SC device 10 in this embodiment is alsodesigned to work with the compression device 90.

An alternate embodiment of the SC device 10 in a preferred embodimentshown in FIGS. 36-54 S also has a male plate 12 and a female plate 14.In addition, the SC device 10 in this embodiment also has a lockingplate 316 and a locking screw 318 that, in combination with standardcancellous bone screws (not shown) fix the SC device 10 to the patient'svertebrae. This SC device 10 has a top side 320, a bottom side 322 andopposed medial sides 324.

The male plate 12 has a male main body 326 and a protrusion 328extending away from the male 0 main body 326. The protrusion 328 has atop surface 330 and a longitudinal axis 332. The male main body 326 isrelatively flat with a top side 334 and a bottom side 336 and, in apreferred embodiment, has two screw receiving holes 338. The screwreceiving holes 338 each have a bowl-shaped basin 340 on the top side334 to receive the heads of the screws and a throughhole 342 throughwhich the main body of the screws pass to come into contact with thevertebral body. The throughholes 342 are machined to have a S rigidrelationship with the bone screws as will be described hereafter.

The bottom side 336 the male plate 12 plate is preferable roughened,thereby allowing the bottom side 336 of male plate 12 to “grip” thevertebral body when the bottom side 336 is brought into contact with andis secured to the vertebral body by the interaction of the screws andthe male main body 326 as described above.

As mentioned, the male plate 12 has a protrusion 328 with a top surface330 and a longitudinal axis 332. Protrusion 328 is dimensioned to matewith and secure the male plate 12 with the female plate 14 as will bedescribed in detail hereafter. The length of protrusion 328 along thelongitudinal axis 332 is chosen to be slightly longer than the distancethe SC device 10 is intended to provide compression over.

Protrusion 328 has a slot 344 extending entirely through itapproximately perpendicular to the top 5 surface 330. Protrusion 328also has a series of alternating ridges 346 and valleys 348,collectively protrusion ridges 350, located on a portion of its topsurface 330. Ridges 350 are preferable angled slightly with respect tothe longitudinal axis 332 for a purpose to be explained hereafter.

The female plate 14 has a female main body 352 with a bottom side 354and a protrusion receiving channel 356. Protrusion receiving channel 356is comprised of a left channel 358, a right channel 360 and a connectingpiece 362. Left channel 358 is basically “C” shaped with a top piece370, bottom piece 372 and an outer piece 374. Although left channel 358has been described as having a top piece 370, bottom piece 372 and outerpiece 374, left channel 358 is preferable a single contiguous piecealthough it could be made of these separate segments connected together.

Right channel 360 has a top piece 370, a bottom piece 372 and an outerpiece 374. Although right channel 360 has been described as having a toppiece 370, bottom piece 372 and outer piece 374, right channel 360, likeleft channel 358, is preferable a single contiguous piece although itcould be made of these separate segments connected together.

Connecting piece 362 connects the left channel 358 to the right channel360 at the respective bottom pieces 372. In the preferred embodiment,connecting piece 362 is integrally formed with the bottom pieces 372although it could be made of these separate segments connected together.Connecting piece 362 has a threaded hole 376 that extends intoconnecting piece 362.

Protrusion receiving channel 356 is dimensioned to snugly receive theprotrusion 328 so that the protrusion 328 is “captured” and held in theprotrusion receiving channel 356 by relatively conformal physicalcontact between the outer surface of the protrusion 328 and the innersurfaces of the left channel 358, right channel 360 and connecting piece362.

The female main body 352 also has an upper surface 378 and a channel 380formed in the upper surface 378 between the left channel 358 and theright channel 360. Channel 380 extends entirely through the uppersurface 378.

The female plate 14, also in a preferred embodiment, has two screwreceiving holes 382. These screw receiving holes 382 receive standardcancellous bone screws (not shown) that are threaded into the bone ofthe vertebrae. In similar fashion to screw receiving holes 338, thescrew receiving holes 382 also have a bowl-shaped basin 384 on the uppersurface 378 to receive the heads of the bone screws and a throughhole386 through which the main body of the bone screws pass to come intocontact with the vertebral body. The throughholes 386 are machined toprovide a rigid relationship with the bone screws.

The SC device 10 has a locking mechanism 388. The locking mechanism 388includes locking plate 316 and locking screw 318 as well as the ridges346 and valleys 348 on the top surface 330 of protrusion 328 of the maleplate 12 and the threaded hole 376 and channel 380 of female plate 14 asdescribed below. Locking mechanism 388 converts “active” compressionapplied by the surgeon using the compression device 90 described aboveinteracting with the SC device 10 at the time of surgery to “static”compression after surgery. The locking mechanism 388 also provides rigidfixation to the SC device 10 to optimize bone healing and preventingfurther settling from occurring.

The locking plate 316 has a top surface 392, a bottom surface 394 andparallel sides 396. The bottom surface of locking plate 316 preferablyhas a series of ridges 398 and valleys 400, collectively locking ridges402, of similar dimensions to the ridges 346 and valleys 348 of theprotrusion 328 to locate and affix the locking plate 316 to theprotrusion 328 as will be described hereafter. In a most preferredembodiment of the invention, the ridges 346 and valleys 348 of theprotrusion 328 and the ridges 398 and valleys 400 of the locking plate316 are angled slightly with respect to the longitudinal axis 332.Through this configuration, the ridges 398 and valleys 400 of the bottomsurface 394 of the locking plate 316 preferably contact and engage withthe ridges 346 and valleys 348 of the protrusion 328 in frictional ormechanical contact to precisely locate and affix the locking plate 316to the protrusion 328. Further, as shown in FIGS. 42 and 48-53, becausethe protrusion ridges 350 and the locking ridges 402 are angled, as thelocking plate 316 is moved from one side of the channel 380 to theother, as the locking ridges 402 seat with the protrusion ridges 350,the male plate 12 is moved into compression with the female plate 14.This compression is transferred through the male plate 12 and femaleplate 14 to the vertebral bone.

The width of the locking plate 316 (i.e, the distance between theparallel sides 396) is such that the locking plate 316 will fit snuglyinto the channel 380 formed in the upper surface 378 of the female plate14 of the SC device 10 but still allow the locking plate 316 to move ina direction perpendicular to the parallel sides 396 within the channel380.

Locking plate 316 has a slot 404. Slot 404 is aligned with channel 344of the protrusion 328 and allows a locking screw 318, as explainedhereafter, to pass through both the slot 404 and mate with the treadedhole 376 as described hereafter. Slot 404 is also dimensioned toconformally mate with the head 406 of screw 318 so that contact betweenthe head 406 and slot 404 as the locking screw 318 is threaded intothreaded hole 376 moves the locking ridges 402 into contact with theprotrusion ridges 350.

A single large locking screw 318 is dimensioned to rotate freely withinthe slot 404 of the locking plate 316 activates the locking mechanism388. In the embodiment of the invention shown in FIGS. 36-54, thelocking screw 318 has a head 406, a threaded body 408 and a distal end410 where the head 406 has a larger cross-sectional diameter than thethreaded body 408.

In use, the protrusion 328 is inserted into the protrusion receivingchannel 356 (FIGS. 39 and 48). Because protrusion receiving channel 356is dimensioned to conformally receive protrusion 328, protrusion isprecisely located and retained within the protrusion receiving channel356. Locking plate 316 is placed on the top surface 330 of protrusion328 within the channel 380 so that the protrusion ridges 350 come intocontact with the locking ridges 402 (FIG. 49). The locking screw 318 ispassed through the slot 404 so that its distal end 410 comes intocontact with and is threaded into the threaded hole 376 a sufficientamount to locate the distal end 410 of the locking screw 318 in thethreaded hole 376 but not a sufficient amount to secure the lockingridges 402 of the locking plate 316 into secure contact with theprotrusion ridges 350 (FIGS. 50-51).

Bone screws are passed through the screw receiving holes 338 and 376 andinto the vertebral bone. These bone screws are screwed into thevertebral bone until the heads of the bone screws seat into the basins334, 378 of the male plate 12 and female plate 14, respectively.

The compression device 90 is then used to apply the desired compressionto the SC device 10. The pins 132 are placed in the notches 442,444 andthe handles 118, 120 are squeezed together. As a result, compressionpressure is applied to the male plate 12 and female plate 14 and therebyto the vertebral bone through the bone screws. As mentioned above, wherea gauge 146 is present, the amount of compressive force applied to theSC device 10 can be ascertained. Once the desired amount of compressiveforce is applied to the device 10, the screwdriver 160 is coupled to thehead 406 of the locking screw 318. The screwdriver 160 is rotated sothat the threaded body 408 of locking screw 318 is threaded into thethreaded hole 376. In this process, the locking ridges 402 are broughtinto secure contact with the protrusion ridges 350. But, to secure anoptimum fit between the locking ridges 402 and the protrusion ridges350, it may be necessary to move the locking plate 316 from side to sidewithin the channel 380 until they mate optimally and impart acompression on the male plate 12 and female plate 14 (FIG. 52). Oncethis optimal mating occurs, the screwdriver 160 is rotated further. Theinteraction between the head 406 and the slot 404 locks the lockingplate 316 against the protrusion 328. Locking screw 318 is tightenedinto tight the threaded hole 376 so that the male plate 12 is securelypositioned with respect to the female plate 14. Once male plate 12 issecured with respect to the female plate 14, the compression device 90is removed.

Another alternate embodiment of the SC device 10 is shown in FIGS.55-56. In this embodiment, the SC device 10 is as described above exceptthat the SC device 10 has a spring mechanism 168 integral between theends of the male plate 12 and female plate 14 that provides a nearconstant force applied to a fixed vertebral segment (or segments)through a standard buttressing or tension band construct. Springmechanism 168 has three parts, a relatively flat spring plate 170, guidepins 184, 186 and a guide plate 172. Spring plate 170 has ends suitablefor attaching to bone via one or more bone screws.

Spring 178 is preferable a plurality of flexible members that resistbeing moved in a lateral direction, in this case, in the direction ofmoving the one plate end 174 away from the other plate end 176. In apreferred version of this embodiment, the spring 178 is a plurality offlat serpentine shaped members made of a spring metal such as springsteel. However, the spring 178 could also be made of a single memberthat has spring-like attributes and could be made of materials otherthan metal so long as the elements of spring 178 possess the ability toresist stretching according to a linear restoring force (i.e., followsHooke's law).

Guide plate 172 reinforces spring plate 170 and provides over extensionprotection as well as flexion/extension moment buffering. Over extensionprotection is provided by guide pins 184, 186 attached to spring plate12 via slots and limit the extension of the spring 178.Flexion/extension is controlled by the guide plate 172 in close contactwith the spring plate 12.

This embodiment of SC device 10 allows the SC device 10 to settle intoposition on the vertebral bone and minimize the deflection of the maleplate 12 and the female plate 14 without a drastic reduction in the SCdevice 10's ability to provide a consistent tension force. Further,after the SC device 10 is implanted, the surgeon can determine theactual level of compression by measuring the overall change in length ofthe construct and applying Hooke's law to determine the relative rate ofcompression.

Another feature of an embodiment of the invention shown in FIG. 57 isthat of a series of trial spacers 202 that include a strain gaugecapable of measuring compressive strain through electromagnetictechniques as are well understood in the art. These spacers 202 arepreferably cylindrical in shape with a handle which allows them to beinserted between the vertebral bodies. The spacers are machined to havethe approximate dimensions of the bone graft which is to be placedbetween adjacent vertebrae (in the disc space once the disc has beenremoved). This embodiment also includes a handle 204 attached to thespacer 202 in order to allow the surgeon ease in facilitating insertionand extraction of the spacer 202. The cylinders of the spacer 202 arepreferably machined in height increments (e.g. one millimeter) in orderto accommodate a variety of disc space heights.

The spacer 202 serves two purposes. First, it enables the surgeon to“size” the disc space in order to place an appropriate sized graft, inthe same manner that many allograft spacers currently have “trials”.Second, each spacer 202 has the characteristics of a strain gauge whichis able to directly measure the “passive” force applied to that spacer202 by the adjacent vertebral bodies, once the spacer 202 is inserted.In this way the surgeon may estimate the approximate “passive” forcewhich would be applied to a similar sized bone graft. The total forceapplied to that graft, then, would be the sum of the passive forceapplied to the graft (as measured by the spacer of similar dimensions)and the active force applied by the surgeon through the compressiondevice 90. Thus, by using the strain-gauge spacer 202 in conjunctionwith the compression device 90, the surgeon may obtain an accurateassessment of total force applied to the graft. This is beneficial inthat it allows further study of the “optimal” force which must beapplied in order to reliably achieve fusion.

In all the embodiments shown, the SC device 10 is a unique device thatutilizes Wolff's law to compress two or more adjacent cervical vertebraewhile fusion between the vertebrae occurs by allowing static, rigidcompression to be applied to interbody graft in the cervical spine.Static, rigid compression has definitively been shown to increase bonyunion in a long bone fracture model. Lumbar interbody fusions have beenshown to heal at a higher rate than intertransverse fusions, presumablybecause of the constant loading of the graft No other currentlyavailable cervical device allows for active, static compression.

It should be noted that use of the SC device 10 is by no means limitedto use in the cervical spine. Any of the aforementioned embodiments, ina somewhat larger version or having a curved bottom side 22 (FIG. 58) aswill be clear to those skilled in the art, may be used for the same orsimilar purposes in the thoracic or lumbar spine, or in instances wherestatic compression is desired outside of the spine (e.g., and withoutlimitation, bone fractures, as for example, of long bones like the femuror bones of the skull, hip or scapula) (FIG. 59).

In the thoracic spine a larger version of the SC device 10 may be placedon the side of the thoracic spine (as opposed to the front) in order tofacilitate approach to the thoracic spine and to avoid large vascularstructures that reside immediately in front of the thoracic spine.

In the lumbar spine, a larger version of the SC device 10 may be placedeither on the side of the spine to facilitate exposure and avoidvascular structures or directly on the front of the spine, especially atthe lumbosacral junction. It is believed that in order to obtainanterior fusion at L5-S1, it is important to have a fully contoured SCdevice 10 (FIG. 58) that is simply comprised of a male plate 12 and afemale plate 14 with a curved bottom side 22 matching the curvature ofthe vertebral segments in the LS-S1 region.

As mentioned above, the SC device 10 may be used to obtain union offractures, nonunions, osteotomies and other bony defects in regionsother than the spine. In the embodiment suited for use with other bones,the SC device 10 should be sized appropriately to the bone and have theoption of placing more than two screws 138 on either side of the defectwhere union is desired (FIG. 59). The SC device 10 allows for maximumutilization of Wolff's Law to facilitate healing in that reproduciblemeasurable compression is applied in each of these scenarios to obtainbony union.

The SC device 10 described herein has the following four uniquecharacteristics which together provide for static compression of thevertebral body-graft interface:

-   -   The use of fixed-angle screws to secure the SC device 10 to the        vertebral bodies;    -   The use of a compression device to apply and measure the        pressure applied to the vertebral bodies by the SC device 10;    -   The technique of using active, static compression to assist the        fusion process; and    -   The use of a locking mechanism 88 that maintains compression        during the fusion process to facilitate bone growth.        These four characteristics of the SC device 10 are not currently        found in any other spinal device. As a result, it is believed        that the SC device 10 in any of the disclosed embodiments        provides an optimal environment for spinal fusions to        consolidate while preventing frequent non-unions and occasional        deformities seen with the use of current dynamic plates.

The SC device 10 in several embodiments has been described in detailabove. However, it is to be understood that the specific features of thevarious components may be modified as will occur to those skilled in theart and still fall within the parameters of the invention. For example,the specific cross-sectional shape of the protrusion 28, left and rightguides 58, 60 and side protrusions 29 may be modified so long as thesecomponents interlock with each other as described herein. Further, theshape of the locking clamp 16 may be modified so long as it is able tobe deformed to force frictional or mechanical contact between thevarious components as described above.

Further, the invention has been described as having a protrusion 28 withside protrusions 29 on a male plate 12 or interconnecting plate IS and aleft guide 58 and right guide 60 on a female plate 14 or interconnectingplate 15. It is clear that the invention could also be practiced withthe male plate 12 or interconnecting plate 15 having a single protrusion28 with the female plate 14 or interconnecting plate 15 still having theleft guide 58 and right guide 60. Also, the SC device 10 could have twoor more protrusions 28 on the male plate 12 or interconnecting plate 15with a corresponding number of protrusion receiving channels 56 toreceive these protrusions 28 and a corresponding number of lockingclamps 16.

The present invention has been described in connection with certainembodiments, configurations and relative dimensions. It is to beunderstood, however, that the description given herein has been givenfor the purpose of explaining and illustrating the invention and are notintended to limit the scope of the invention. For example, complimentaryversions of the mating aspects of the SC device 10 could be formed andstill be within the scope of the invention. In addition, it is clearthan an almost infinite number of minor variations to the form andfunction of the disclosed invention could be made and also still bewithin the scope of the invention. Consequently, it is not intended thatthe invention be limited to the specific embodiments and variants of theinvention disclosed. It is to be further understood that changes andmodifications to the descriptions given herein will occur to thoseskilled in the art. Therefore, the scope of the invention should belimited only by the scope of the claims.

1. A method of fusing adjacent vertebrae comprising the steps of: (a)providing active, controlled compression between a first plate having afirst longitudinal axis, and a second plate having a second longitudinalaxis wherein the first plate and the second plate move relative to eachother when their respective axes are commonly aligned, wherein the firstplate and second plate have a locking mechanism to precisely locate thefirst plate with respect to the second plate, and wherein the firstplate is attachable to a first vertebrae and the second plate isattachable to a second vertebrae; (b) attaching the first plate to afirst vertebrae; (c) attaching the second plate to a second vertebrae;and (d) applying compression to the device so that compression istransferred to the first and second vertebrae.
 2. The method of claim 1,wherein the step of providing includes providing active, controlledcompression between the first plate, the second plate, and one or moreinterconnecting plates, the one or more interconnecting plates having athird longitudinal axis wherein the first plate, second plate, and theone or more interconnecting plates move relative to each other whentheir respective axes are commonly aligned, and wherein the first plate,second plate, and the one or more interconnecting plates each have alocking mechanism to precisely locate the first plate with respect tothe one or more interconnecting plates, the one or more interconnectingplates with respect to each other, and the second plate with respect tothe one or more interconnecting plates, and wherein the first plate isattachable to a first vertebrae, the second plate is attachable to asecond vertebrae, and the one or more interconnecting plates areattached to one or more vertebrae, respectively, between the first andsecond vertebrae.
 3. The method of claim 1, wherein the step ofproviding a device comprises the further steps of: (a) providing a maleplate with a male main body with a bottom side and a central protrusionextending away from the male main body, the male plate having a fourthlongitudinal axis; (b) providing a female plate having a female mainbody with a bottom side and a protrusion receiving channel adapted toconformally receive the central protrusion, the female plate having afifth longitudinal axis, wherein the fourth longitudinal axis of themale plate is aligned with the fifth longitudinal axis of the femaleplate when the protrusion receiving channel receives the centralprotrusion; and (c) providing a locking mechanism for allowing the maleand the female plate to move with respect to each other undercompression along their aligned fourth and fifth longitudinal axes whenthe central protrusion is engaged with the protrusion receiving channeluntil a desired configuration is achieved, and thereafter to prevent themale and female plate from moving with respect to each other.
 4. Themethod of claim 3, further comprising the step of: (d) providing acompression device for providing active, controlled compression betweenthe male plate and the female plate, the compression device comprising:(i) a first arm with a proximal end and a distal end, the proximal endhaving a handle and the distal end having a foot, the foot adapted tosecurely connect the distal end of the first arm to the male plate; (ii)a second with a proximal end and a distal end, the proximal end having ahandle and the distal end having a foot, the foot adapted to securelyconnect the distal end of the second arm to the female plate; (iii) apivot pivotally connecting the first arm to the second aim so that thefirst arm and second arm may move in scissors-like movement with respectto each other, (iv) a central processing unit capable of calculating, byrunning a formula, the force corresponding to electrical resistanceacross a strain gauge or of looking up values of force corresponding todetected electrical resistance across a strain gauge; (v) a displayconnected to the central processing unit to indicate the amount of forceapplied in either compression or distraction by the compression device;(vi) a strain gauge, connected to the central processing unit, that issecured to either the first or second arm of the compression device; and(vii) a turnbuckle located between and attached to either the handles ofthe first or second arms of the compression device or between the distalends of the first and second arms of the compression device, whereinrotation of the turnbuckle in a first direction moves, respectively, thehandles apart from each other or the distal ends apart from each other,and wherein rotation of the turnbuckle in a second direction oppositethe first direction moves, respectively, the handles toward each otheror the distal ends toward each other, wherein the central processingunit measures the resistance across the strain gauge and thendetermines, by formula or through a lookup table, the amount of forceapplied in distraction or compression by the compression device, andthen indicates the amount of force on the display, whereby, a surgeonsqueezing the handles on the first arm and the second arm moves thedistal ends of the first arm and the second arm together therebyapplying compression to the male plate and female plate, and thus toadjacent respective vertebrae, through the interaction of the feet andthe respective male plate and female plate.
 5. The method of claim 4,further comprising the step of: (e) providing a zeroing function systemcomprising means for communicating to the central processing unit thatsufficient distraction has been applied by the compression device tovertebrae connected to the device to establish lift-off of vertebrae towhich the device is attached.
 6. The method of claim 5, furthercomprising the steps of: (f) displaying on the display, under directionby the central processing unit, a null value upon communication to thecentral processing unit that sufficient distraction has been applied bythe compression device to vertebrae connected to the device to establishlift-off of vertebrae to which the device is attached and thereafter;and (g) displaying on the display, under direction by the centralprocessing unit, the value of the force applied anatomically and by thecompression device to vertebrae to which the device is attached.
 7. Themethod of claim 4, wherein the step of providing a compression devicefurther comprises the step of providing a zeroing function systemcomprising means for communicating to the central processing unit thatno distraction has been applied by the compression device to vertebraeto which the device is attached.
 8. The method of claim 7, furthercomprising the steps of: (h) displaying on the display, under directionby the central processing unit, a null value upon communication to thecentral processing unit that no distraction has been applied by thecompression device to vertebrae to which the device is attached andthereafter; and (i) displaying on the display, under direction by thecentral processing unit, the value of the force applied throughdistraction or compression by the compression device to vertebrae towhich the device is attached.
 9. A method of determining and displayinga total amount of compression force applied, both anatomically and by asurgeon, to vertebrae, comprising the steps of: (a) applying distractionforce to the vertebrae until the vertebrae experience lift-off; (b)measuring and displaying the amount of distraction force in step (a);(c) setting the displayed value of the force applied to the vertebrae tozero; (d) removing the distraction force applied to the vertebrae instep (a); (e) displaying the amount of force anatomically applied to thevertebrae; (f) applying compression force to the vertebrae; and (g)displaying the combined amount of force applied anatomically and in step(f) to the vertebrae.
 10. A method of compressing two or more adjacentpieces of bone comprising the steps of: (a) providing a device forproviding active, controlled compression between a first plate having alongitudinal axis and a second plate having a longitudinal axis whereinthe first plate and the second plate move relative to each other whentheir axes are commonly aligned and wherein the first plate and secondplate have a locking mechanism to precisely locate the first plate withrespect to the second plate and wherein the first plate is attachable toa first piece of bone and the second plate is attachable to a secondpiece of bone; (b) attaching the first plate to a first piece of bone;(c) attaching the second plate to a second piece of bone; (d) applyingcompression to the device so that compression is transferred to thefirst and second pieces of bone.
 11. The method of claim 10, wherein:the step of providing a device includes the step of providing a devicefor providing active, controlled compression between a first platehaving a longitudinal axis, a second plate having a longitudinal axis,and one or more interconnecting plates, each of the one or moreinterconnecting plates having a longitudinal axis; the first plate,second plate, and one or more interconnecting plates move relative toeach other when their respective axes are commonly aligned; the firstplate, second plate, and one or more interconnecting plates each have alocking mechanism to precisely locate the first plate with respect tothe one or more interconnecting plates, the one or more interconnectingplates with respect to another of the one or more interconnectingplates, and the second plate with respect to the one or moreinterconnecting plates; and the first plate is attachable to a firstpiece of bone, the second plate is attachable to a second piece of bone,and the one or more interconnecting plates are attached to one or morepieces of bone, respectively, between the first and second pieces ofbone.
 12. The method of claim 10, wherein the step of providing furthercomprises the steps of: (a) providing a male plate having a male mainbody including a bottom side thereof, the male plate further having alongitudinal axis and a central protrusion extending away from the malemain body; (b) providing a female plate having a female main bodyincluding a bottom side thereof, the female plate further having alongitudinal axis and a protrusion receiving channel adapted toconformally receive the central protrusion of the male plate; and (c)providing a locking mechanism for allowing the male and female plate tomove with respect to each other under compression along a commonlongitudinal axis when the central protrusion is engaged with theprotrusion receiving channel until a desired configuration is achievedand thereafter to prevent the male and female plate from moving withrespect to each other, wherein the longitudinal axis of the male plateis aligned with the longitudinal axis of the female plate, when theprotrusion receiving channel receives the central protrusion, to formthe common longitudinal axis.
 13. The method of claim 3, wherein thelocking mechanism is selectable between locked and unlockedconfigurations, to operate in either static or dynamic modes,respectively.
 14. The method of claim 1, comprising the further step of:(e) fixedly locking the first and second plates with respect to oneanother.
 15. The method of claim 14, comprising the further step of (f)removing the active, controlled compression between the first and secondplates.
 16. The method of claim 1, wherein the active, controlledcompression is provided by a cantilever displacement arm adjacent thefirst and second plates.